Showing papers in "Astronomy and Astrophysics in 2003"

A synthetic view on structure and evolution of the Milky Way

Abstract: Since the Hipparcos mission and recent large scale surveys in the optical and the near-infrared, new constraints have been obtained on the structure and evolution history of the Milky Way. The population synthesis approach is a useful tool to interpret such data sets and to test scenarios of evolution of the Galaxy. We present here new constraints on evolution parameters obtained from the Besancon model of population synthesis and analysis of optical and near-infrared star counts. The Galactic potential is computed self-consistently, in agreement with Hipparcos results and the observed rotation curve. Constraints are posed on the outer bulge structure, the warped and flared disc, the thick disc and the spheroid populations. The model is tuned to produce reliable predictions in the visible and the near-infrared in wide photometric bands from U to K. Finally, we describe applications such as photometric and astrometric simulations and a new classification tool based on a Bayesian probability estimator, which could be used in the framework of Virtual Observatories. As examples, samples of simulated star counts at different wavelengths and directions are also given.

Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458

Abstract: We present evolutionary models for cool brown dwarfs and extra-solar giant planets. The models reproduce the main trends of observed methane dwarfs in near-IR color-magnitude diagrams. We also present evolutionary models for irradiated planets, coupling for the first time irradiated atmosphere profiles and inner structures. We focus on HD 209458-like systems and show that irradiation effects can substantially affect the radius of sub-jovian mass giant planets. Irradiation effects, however, cannot alone explain the large observed radius of HD 209458b. Adopting assumptions which optimise irradiation effects and taking into account the extension of the outer atmospheric layers, we still find $\\sim$ 20% discrepancy between observed and theoretical radii. An extra source of energy seems to be required to explain the observed value of the first transit planet.

The INTEGRAL mission

Abstract: The ESA observatory INTEGRAL (International Gamma-Ray Astrophysics Laboratory) is dedicated to the fine spectroscopy (2.5 keV FWHM @ 1 MeV) and fine imaging (angular resolution: 12 arcmin FWHM) of celestial gamma-ray sources in the energy range 15 keV to 10 MeV with concurrent source monitoring in the X-ray ( keV) and optical (V -band, 550 nm) energy ranges. INTEGRAL carries two main gamma-ray instruments, the spectrometer SPI (Vedrenne et al. [CITE]) – optimized for the high-resolution gamma-ray line spectroscopy (20 keV–8 MeV), and the imager IBIS (Ubertini et al. [CITE]) – optimized for high-angular resolution imaging (15 keV–10 MeV). Two monitors, JEM-X (Lund et al. [CITE]) in the () keV X-ray band, and OMC (Mas-Hesse et al. [CITE]) in optical Johnson V -band complement the payload. The ground segment includes the Mission Operations Centre at ESOC, ESA and NASA ground stations, the Science Operations Centre at ESTEC and the Science Data Centre near Geneva. INTEGRAL was launched on 17 October 2002. The observing programme is well underway and sky exposure (until June 2003) reaches ~1800 ks in the Galactic plane. The prospects are excellent for the scientific community to observe the high energy sky using state-of-the-art gamma-ray imaging and spectroscopy. This paper presents a high-level overview of INTEGRAL.

IBIS: The Imager on-board INTEGRAL

Abstract: The IBIS telescope is the high angular resolution gamma-ray imager on-board the INTEGRAL Observatory, suc- cessfully launched from Baikonur (Kazakhstan) the 17th of October 2002. This medium size ESA project, planned for a 2 year mission with possible extension to 5, is devoted to the observation of the gamma-ray sky in the energy range from 3 keV to 10 MeV (Winkler 2001). The IBIS imaging system is based on two independent solid state detector arrays optimised for low (15 1000 keV) and high (0:175 10:0 MeV) energies surrounded by an active VETO System. This high eciency shield is essential to minimise the background induced by high energy particles in the highly excentric out of van Allen belt orbit. A Tungsten Coded Aperture Mask, 16 mm thick and1 squared meter in dimension is the imaging device. The IBIS telescope will serve the scientific community at large providing a unique combination of unprecedented high energy wide field imaging capability coupled with broad band spectroscopy and high resolution timing over the energy range from X to gamma rays. To date the IBIS telescope is working nominally in orbit since more than 9 month.

Hyperleda. I. Identification and designation of galaxies

Abstract: We present the new catalog of principal galaxies (PGC2003). It constitutes the framework of the HYPERLEDA database that supersedes the LEDA one, with more data and more capabilities. The catalog is still restricted to confirmed galaxies, i.e. about one million galaxies, brighter than similar to 18 B-mag. In order to provide the best possible identification for each galaxy we give: accurate coordinates ( typical accuracy better than 2 arcsec), diameter, axis ratio and position angle. Diameters and axis ratios have been homogenized to the RC2 system at the limiting surface brightness of 25B - mag arcsec(-2), using a new method, the EPIDEMIC method. In order to provide the best designation for each galaxy, we collected the names from 50 catalogues. The compatibility of the spelling is tested against NED and SIMBAD, and, as far as possible we used a spelling compatible with both. For some cases, where no consensus exists between NED, SIMBAD and LEDA, we propose some changes that could make the spelling of names fully compatible. The full catalog is distributed through the CDS and can be extracted from HYPERLEDA.

The stellar activity-rotation relationship revisited: Dependence of saturated and non-saturated X-ray emission regimes on stellar mass for late-type dwarfs ?

Abstract: We present the results of a new study on the relationship between coronal X-ray emission and stellar rotation in late-type main-sequence stars. We have selected a sample of 259 dwarfs in the B V range 0.5-2.0, including 110 field stars and 149 members of the Pleiades, Hyades, Persei, IC 2602 and IC 2391 open clusters. All the stars have been observed with ROSAT, and most of them have photometrically-measured rotation periods available. Our results confirm that two emission regimes exist, one in which the rotation period is a good predictor of the total X-ray luminosity, and the other in which a constant saturated X-ray to bolometric luminosity ratio is attained; we present a quantitative estimate of the critical rotation periods below which stars of dierent masses (or spectral types) enter the saturated regime. In this work we have also empirically derived a characteristic time scale,e, which we have used to investigate the relationship between the X-ray emission level and an X-ray-based Rossby number Re = Prot=e: we show that our empirical time scalee resembles the theoretical convective turnover time for 0:4 M=M 1:2, but it also has the same functional dependence on B V as L 1=2 bol in the color range 0:5 B V 1:5. Our results imply that - for non-saturated coronae - the Lx - Prot relation is equivalent to the Lx=Lbol vs. Re relation.

Elemental abundance trends in the Galactic thin and thick disks as traced by nearby F and G dwarf stars

Abstract: Based on spectra from F and G dwarf stars, we present elementalabundance trends in the Galactic thin and thick disks in the metallicityregime -0.8< [Fe/H < +0.4. Our findings can besummarized as follows. 1) Both the thin and the thick disks show smoothand distinct abundance trends that, at sub-solar metallicities, areclearly separated. 2) For the alpha -elements the thick disk showssignatures of chemical enrichment from SNe type Ia. 3) The age of thethick disk sample is in the mean older than the thin disk sample. 4)Kinematically, there exist thick disk stars with super-solarmetallicities. Based on these findings, together with other constraintsfrom the literature, we discuss different formation scenarios for thethick disk. We suggest that the currently most likely formation scenariois a violent merger event or a close encounter with a companion galaxy.Based on kinematics the stellar sample was selected to contain starswith high probabilities of belonging either to the thin or to the thickGalactic disk. The total number of stars are 66 of which 21 belong tothe thick disk and 45 to the thin disk. The analysis is based onhigh-resolution spectra with high signal-to-noise (R 48 000 and S/Ngtrsim 150, respectively) recorded with the FEROS spectrograph on LaSilla, Chile. Abundances have been determined for four alpha -elements(Mg, Si, Ca, and Ti), for four even-nuclei iron peak elements (Cr, Fe,Ni, and Zn), and for the light elements Na and Al, from equivalent widthmeasurements of 30 000 spectral lines. An extensive investigation ofthe atomic parameters, log gf-values in particular, have been performedin order to achieve abundances that are trustworthy. Noteworthy is thatwe find for Ti good agreement between the abundances from Ti I and TiIi. Our solar Ti abundances are in concordance with the standardmeteoritic Ti abundanceBased on observations collected at the European Southern Observatory, LaSilla, Chile, Proposals #65.L-0019(B) and 67.B-0108(B).Full Tables eftab:linelist and eftab:abundances are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/527 (Less)

ISGRI: The INTEGRAL soft gamma-ray imager

Abstract: For the first time in the history of high energyastronomy, a large CdTe gamma-ray camera is operating in space. ISGRI is the low-energy camera of the IBIS telescope on board the INTEGRAL satellite. This paper details its design and itsin-flight behavior and performances. Having a sensitive area of 2621 cm$^2$ with a spatial resolution of 4.6 mm, a low threshold around 12 keV and an energy resolution of $\sim$ 8\% at 60 keV, ISGRI shows absolutely no signs of degradation after 9 months in orbit. All aspects of its in-flight behavior and scientific performance are fully nominal, and in particular the observedbackground level confirms the expected sensitivity of 1 milliCrab for a 10$^6$s observation.

The 2-10 keV luminosity as a Star Formation Rate indicator

Abstract: Radio and far infrared luminosities of star-forming galaxies follow a tight linear relation. Making use of ASCA and BeppoSAX observations of a well-defined sample of nearby star-forming galaxies, we argue that tight linear relations hold between the X-ray, radio and far infrared luminosities. The effect of intrinsic absorption is investigated taking NGC3256 as a test case. It is suggested that the hard X-ray emission is directly related to the Star Formation Rate. Star formation processes may also account for most of the 2-10 keV emission from LLAGNs of lower X-ray luminosities (for the same FIRand radio luminosity). Deep Chandra observations of a sample of radio-selected star-forming galaxies in the Hubble Deep Field North show that the same relation holds also at high (0.2 < z < 1.3) redshift. The X-ray/radio relations also allow a derivation of X-ray number counts up to very faint fluxes from the radio Log N-Log S, which is consistent with current limits and models. Thus the contribution of star-forming galaxies to the X-ray background can be estimated.

Catalogue of cataclysmic binaries, low-mass X-ray binaries and related objects (Seventh edition)

Abstract: The catalogue lists coordinates, apparent magnitudes, orbital parameters, and stellar parameters of the compo- nents and other characteristc properties of 472 cataclysmic binaries, 71 low-mass X-ray binaries and 113 related objects with known or suspected orbital periods together with a comprehensive selection of the relevant recent literature. In addi- tion, the catalogue contains a list of references to published finding charts for 635 of the 656 objects, and a cross-reference list of alias object designations. Literature published before 1 January 2003 has, as far as possible, been taken into ac- count. All data can be accessed via the dedicated catalogue webpage at http://www.mpa-garching.mpg.de/RKcat/ and http://physics.open.ac.uk/RKcat/ and at CDS via anonymous ftp to cdsarc.u-strasbg.fr (30.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/301. We will update the information given on the catalogue webpage regularly, initially every six months.

SPI: The spectrometer aboard INTEGRAL

Abstract: SPI is a high spectral resolution gamma-ray telescope on board the ESA mission INTEGRAL (International Gamma Ray Astrophysics Laboratory). It consists of an array of 19 closely packed germanium detectors surrounded by an active anticoincidence shield of BGO. The imaging capabilities of the instrument are obtained with a tungsten coded aperture mask located 1.7 m from the Ge array. The fully coded field-of-view is 16degrees, the partially coded field of view amounts to 31degrees, and the angular resolution is 2.5degrees. The energy range extends from 20 keV to 8 MeV with a typical energy resolution of 2.5 keV at 1.3 MeV. Here we present the general concept of the instrument followed by a brief description of each of the main subsystems. INTEGRAL was successfully launched in October 2002 and SPI is functioning extremely well.

Rosseland and Planck mean opacities for protoplanetary discs

Abstract: In this paper, we present mean gas and dust opacities relevant to the physical conditions typical of protoplanetary discs. As the principal absorber for temperatures below ∼1500 K, we consider spherical and aggregate dust particles of various sizes, chemical structure, and porosity, consisting of ice, organics, troilite, silicates, and iron. For higher temperatures, ions, atoms, molecules, and electrons are included as the main opacity sources. Rosseland and Planck mean opacities are calculated for temperatures between 5 K and 10 000 K and gas densities ranging from 10 −18 gc m −3 to 10 −7 gc m −3 . The dependence on the adopted model of dust grains is investigated. We compare our results with recent opacity tables and show how different opacity models affect the calculated hydrodynamical structure of accretion discs.

The transition from Population III to normal galaxies: Lyα and He II emission and the ionising properties of high redshift starburst galaxies

Abstract: Using new sets of stellar evolution models at very low metallicities (Z = 10 −7 ,1 0 −5 ) and previously published grids we examine spectral properties of the ionising continua, the Lyman-break, and the Lyα and He  λ1640 recombination lines in starbursts. The metallicity dependence of these properties, especially the transition from primordial galaxies (Population III) to currently observed metallicities, is examined for various IMFs and star formation histories. For the average properties of starbursts, approximated by a model with constant star formation, the main findings are: - The Lyman continuum flux Q(H) increases with decreasing metallicity. For a universal Salpeter IMF from 1-100 Mthe enhancement reaches typically a factor of ∼3 between solar metallicity and Pop III objects. - While for metallicities Z > 1/50 Zthe amplitude of the Lyman-break depends little on Z, a reduction by a factor ∼ 2i s found at lower metallicities, due to the strong increase of the average stellar temperature. - Using theoretical models and empirical constraints we discuss the expected evolution of the hardness of He + to H ionising photons, Q(He + )/Q(H), with metallicity and possible uncertainties. Over the metallicity range Z = 0t o∼10 −4 the hardness decreases from log(Q(He + )/Q(H)) ∼− 1.4 .. .−2.3 by ∼1.5-2 or more orders of magnitude, depending strongly on the upper mass cut-off of the IMF. From empirical constraints we derive a hardness log(Q(He + )/Q(H)) ∼ -3.2 to -2.6 for metal-poor starbursts (1/25 1/50 Zto 400-850 A or higher at Z between 10 −5 and 0 (Pop III) for the same Salpeter IMF. However, for well known reasons, the Lyα emission predicted likely represents an upper limit. Non-negligible He  λ1640 emission due to stellar photoionisation appears to be limited to very small metallicities (log(Z/Z� ) < −5.3) and Population III objects. The predictions, available on the Web through the CDS and at http://webast.ast.obs-mip.fr/sfr/, should be useful for a variety of studies regarding high redshift galaxies, cosmological reionisation, and others.

Stellar evolution with rotation X: Wolf-Rayet star populations at solar metallicity

Abstract: We examine the properties of Wolf-Rayet (WR) stars predicted by models of rotating stars taking account of the new mass loss rates for O-type stars and WR stars (Vink et al. 2000. 2001; Nugis & Lamers 2000) and of the wind anisotropies induced by rotation. We find that the rotation velocities v of WR stars are modest, i.e. about 50 km s - 1 , not very dependent on the initial ν and masses. For the most massive stars, the evolution of ν is very strongly influenced by the values of the mass loss rates; below 12 M O . the evolution of rotation during the MS phase and later phases is dominated by the internal coupling. Massive stars with extreme rotation may skip the LBV phase. Models having a typical v for the O-type stars have WR lifetimes on the average two times longer than for non-rotating models. The increase of the WR lifetimes is mainly due to that of the H-rich eWNL phase. Rotation allows a transition WN/WC phase to be present for initial masses lower than 60 M O .. The durations of the other WR subphases are less affected by rotation. The mass threshold for forming WR stars is lowered from 37 to 22 M O . for typical rotation. The comparisons of the predicted number ratios WR/O, WN/WC and of the number of transition WN/WC stars show very good agreement with models with rotation, while this is not the case for models with the present-day mass loss rates and no rotation. As to the chemical abundances in WR stars, rotation brings only very small changes for WN stars, since they have equilibrium CNO values. However, WC stars with rotation have on average lower C/He and O/He ratios. The luminosity distribution of WC stars is also influenced by rotation.

Star-forming complexes and the spiral structure of our Galaxy

Abstract: We have carried out a multiwavelength study of the plane of our Galaxy in order to establish a star-forming-complex catalogue which is as complete as possible. Features observed include H, H109, CO, the radio continuum and absorption lines. For each complex we have determined the position, the systemic velocity, the kinematic distance and, when possible, the stellar distance and the corresponding uncertainties. All of these parameters were determined as homogeneously as possible, in particular all the stellar distances have been (re)calculated with the same calibration and the kinematic distances with the same mean Galactic rotation curve. Through the complexes with stellar distance determination, a rotation curve has been fitted. It is in good agreement with the one of Brand & Blitz (1993). We also investigated the residual velocities relative to the circular rotation model. We find that departures exist over large areas of the arms, with dierent values from one arm to another. From our data and in good agreement with previous studies, the Galactic warp is observed. It does not seem correlated with the departures from circular rotation. Finally, as segment-like features are noted from the complexes' distribution, we tried to find if they are indicative of a larger underlying structure. Then, we attempted to interpret the complexes' distribution in terms of spiral structure by fitting models with two, three and four logarithmic spiral arms. The four-arm model seems more appropriate to represent the grand design of our Galaxy. In this model the Norma arm and the external arm appear as being the two extremities of a single arm called the Norma-Cygnus arm. The new data and fitted model confirm the four-segment model of Georgelin & Georgelin (1976), clarifying the arms' design and extension and doubling their known length.

JEM-X: The X-ray monitor aboard INTEGRAL ?

Abstract: The JEM-X monitor provides X-ray spectra and imaging with arcminute angular resolution in the 3 to 35 keV band. The good angular resolution and the low energy response of JEM-X plays an important role in the identification of gamma ray sources and in the analysis and scientific interpretation of the combined X-ray and gamma ray data. JEM-X is a coded aperture instrument consisting of two identical, coaligned telescopes. Each of the detectors has a sensitive area of 500 cm 2 , and views the sky through its own coded aperture mask. The two coded masks are inverted with respect to each other and provides an angular resolution of 3 0 across an eective field of view of about 10 diameter.

Age and Metallicity Distribution of the Galactic Bulge from Extensive Optical and Near-IR Stellar Photometry

Abstract: We present a new determination of the metallicity distribution, age, and luminosity function of the Galactic bulge stellar population. By combining near-IR data from the 2MASS survey, from the SOFI imager at ESO NTT and the NICMOS camera on board HST we were able to construct color-magnitude diagrams (CMD) and luminosity functions (LF) with large statistics and small photometric errors from the Asymptotic Giant Branch (AGB) and Red Giant Branch (RGB) tip down to ∼0.15 M� . This is the most extended and complete LF so far obtained for the galactic bulge. Similar near-IR data for a disk control field were used to decontaminate the bulge CMDs from foreground disk stars, and hence to set a stronger constraint on the bulge age, which we found to be as large as that of Galactic globular clusters, or >10 Gyr. No trace is found for any younger stellar population. Synthetic CMDs have been constructed to simulate the effect of photometric errors, blending, differential reddening, metallicity dispersion and depth effect in the comparison with the observational data. By combining the near-IR data with optical ones, from the Wide Field Imager at the ESO/MPG 2.2 m telescope, a disk-decontaminated (MK,V-K )C MD has been constructed and used to derive the bulge metallicity distribution, by comparison with empirical RGB templates. The bulge metallicity is found to peak at near solar value, with a sharp cutoff just above solar, and a tail towards lower metallicity that does not appreciably extend below (M/H) ∼− 1.5.

STELIB: A library of stellar spectra at R 2000 ?;??

Abstract: We present STELIB ? , a new spectroscopic stellar library, available at http://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneous library of 249 stellar spectra in the visible range (3200 to 9500 A), with an intermediate spectral resolution (<3 A) and sampling (1 A). This library includes stars of various spectral types and luminosity classes, spanning a relatively wide range in metallicity. The spectral resolution, wavelength and spectral type coverage of this library represents a substantial improvement over previous libraries used in population synthesis models. The overall absolute photo- metric uncertainty is 3%.

The COMBO-17 survey: Evolution of the galaxy luminosity function from 25,000 galaxies with 0.2 < z < 1.2

Abstract: We present a detailed empirical assessment of how the galaxy luminosity function and stellar luminosity density evolves over the last half of the universe's age (0.2 < z < 1.2) for galaxies of different spectral energy distributions (SED). The results are based on ∼25 000 galaxies (R < 24) with redshift measurements (σz ≈ 0.03) and SEDs across λobs ≈ 350 ... 930 nm. The redshifts and SEDs were derived from medium-band photometry in 17 filters, observed as part of the COMBO-17 survey ("Classifying Objects by Medium-Band Observations in 17 Filters") over three disjoint fields with a total area of 0.78 square degrees. Luminosity functions (LF), binned in redshift and SED-type, are presented in the restframe passbands of the SDSS r-band, the Johnson B-band and a synthetic UV continuum band at 280 nm. We find that the luminosity function depends strongly on SED-type at all redshifts covered. The shape of the LF, i.e. the faint-end power-law slope, does depend on SED type, but not on redshift. However, the redshift evolution of the characteristic luminosity M ∗ and density φ ∗ depends strongly on SED-type: (1) Early-type galaxies, defined as redder than a present-day reference Sa spectrum, become drastically more abundant towards low redshift, by a factor of 10 in the number density φ ∗ from z = 1.1 to now, and by a factor of 4 in their contribution to the co-moving r-band luminosity density, jr. (2) Galaxies resembling present-day Sa- to Sbc-colours show a co-moving number density and contribution to jr that does not vary much with redshift. (3) Galaxies with blue spectra reflecting strong star formation decrease towards low redshift both in luminosity and density, and by a factor of 4 in their jr contribution. Summed over all SED types and galaxy luminosities, the comoving luminosity density decreases towards low redshift, between z = 1.1 and now, by a small amount in restframe r and B, but by a factor of ∼6 in restframe 280 nm. At z = 1.1, galaxies redder than Sbc's, contribute 40% to the total jr, which increases to 75% by z = 0. For λrest =280 nm, this increase is from 12% to 25% over the same redshift interval. Comparison of the three independent sight-lines shows that our results are not significantly affected by large-scale structure. Our lowest redshift bin at z = (0.2, 0.4) largely agrees with the recent assessment of the present-day galaxy population by SDSS and 2dFGRS and deviates only by an excess of "faint blue galaxies" at z ∼ 0.3 compared to very local samples. Overall our findings provide a set of new and much more precise constraints to model the waning of overall star formation activity, the demise of star-bursts and the strong emergence of "old" galaxies, with hardly any young population, over the last 6-8 Gigayears.

A three-dimensional Galactic extinction model

Abstract: A large-scale three-dimensional model of Galactic extinction is presented based on the Galactic dust distribution model of Drimmel & Spergel (2001). The extinction A V to any point within the Galactic disk can be quickly deduced using a set of three-dimensional Cartesian grids. Extinctions from the model are compared to empirical extinction measures, including lines-of-sight in and near the Galactic plane using optical and NIR extinction measures: in particular we show how extinction can be derived from NIR color-magnitude diagrams in the Galactic plane to a distance of 8 kiloparsec.

Spectral and photometric evolution of young stellar populations: The impact of gaseous emission at various metallicities

Abstract: We include gaseous continuum and line emission into our galev models for the spectral and photometric evolution of Simple Stellar Populations (SSPs) for various metallicities in the range 0:02 Z=Z 2:5. This allows to extend them to significantly younger ages than before. They now cover the age range from 4 Myr all through 14 Gyr. We point out the very important contributions of gaseous emission to broad band fluxes and their strong metallicity dependence during very early evolutionary stages of star clusters, galaxies or subgalactic fragments with vigorous ongoing star formation. Emission- line contributions are commonly seen in these actively star-forming regions. Models without gaseous emission cannot explain their observed colors at all, or lead to wrong age estimates. We use up-to-date Lyman continuum (=Lyc) emission rates and decided to use recent empirical determinations of emission line ratios relative to H for subsolar metallicities. We justify this approach for all situations where no or not enough spectral information is available to determine all the parameters required by photoionization models. The eects of gaseous line and continuum emission on broad band fluxes are shown for dierent metallicities and as a function of age. In addition to the many filter systems already included in our earlier models, we here also include the HST NICMOS and Advanced Camera for Surveys (=ACS) filter systems.

The INTEGRAL Science Data Centre (ISDC)

Abstract: The INTEGRAL Science Data Centre (ISDC) provides the INTEGRAL data and means to analyse them to the scientific community. The ISDC runs a gamma ray burst alert system that provides the position of gamma ray bursts on the sky within seconds to the community. It operates a quick-look analysis of the data within few hours that detects new and unexpected sources as well as it monitors the instruments. The ISDC processes the data through a standard analysis the results of which are provided to the observers together with their data.

Radio/X-ray correlation in the low/hard state of GX 339-4

Abstract: We present the results of a long-term study of the black hole candidate GX 339 4 using simultaneous radio (from the Australia Telescope Compact Array) and X-ray (from the Rossi X-ray Timing Explorer and BeppoSAX) observations performed between 1997 and 2000. We find strong evidence for a correlation between these two emission regimes that extends over more than three decades in X-ray flux, down to the quiescence level of GX 339 4. This is the strongest evidence to date for such strong coupling between radio and X-ray emission. We discuss these results in light of a jet model that can explain the radio/X-ray correlation. This could indicate that a significant fraction of the X-ray flux that is observed in the low-hard state of black hole candidates may be due to optically thin synchrotron emission from the compact jet.

Photospheric radius expansion X-ray bursts as standard candles

Abstract: We examined the maximum bolometric peak luminosities during type I X-ray bursts from the persistent or transient luminous X-ray sources in globular clusters. We show that for about two thirds of the sources the maximum peak luminosities during photospheric radius expansion X-ray bursts extend to a critical value of 3:790:1510 38 erg s 1 , assuming the total X-ray burst emission is entirely due to black-body radiation and the recorded maximum luminosity is the actual peak luminosity. This empirical critical luminosity is consistent with the Eddington luminosity limit for hydrogen poor material. Since the critical luminosity is more or less always reached during photospheric radius expansion X-ray bursts (except for one source), such bursts may be regarded as empirical standard candles. However, because significant deviations do occur, our standard candle is only accurate to within 15%. We re-evaluated the distances to the twelve globular clusters in which the X-ray bursters reside.

3D mapping of the dense interstellar gas around the Local Bubble

Abstract: We present intermediate results from a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, motivated by the availability of accurate and consistent parallaxes from the Hipparcos satellite. Equivalent widths of the interstellar NaI D-line doublet at 5890 A are presented for the lines-of-sight towards some 311 new target stars lying within ∼350 pc of the Sun. Using these data, together with NaI absorption measurements towards a fur- ther ∼240 nearby targets published in the literature (for many of them, in the directions of molecular clouds), and the ∼450 lines- of-sight already presented by (Sfeir et al. 1999), we show 3D absorption maps of the local distribution of neutral gas towards 1005 sight-lines with Hipparcos distances as viewed from a variety of different galactic projections. The data are synthesized by means of two complementary methods, (i) by mapping of iso-equivalent width contours, and (ii) by density distribution calculation from the inversion of column-densities, a method devised by Vergely et al. (2001). Our present data confirms the view that the local cavity is deficient in cold and neutral interstellar gas. The closest dense and cold gas "wall", in the first quadrant, is at ∼55-60 pc. There are a few isolated clouds at closer distance, if the detected absorption is not produced by circumstellar material. The maps reveal narrow or wide "interstellar tunnels" which connect the Local Bubble to surrounding cavities, as predicted by the model of Cox & Smith (1974). In particular, one of these tunnels, defined by stars at 300 to 600 pc from the Sun showing negligible sodium absorption, connects the well known CMa void (Gry et al. 1985), which is part of the Local Bubble, with the supershell GSH 238+00+09 (Heiles 1998). High latitude lines-of-sight with the smallest absorption are found in two "chimneys", whose directions are perpendicular to the Gould belt plane. The maps show that the Local Bubble is "squeezed" by surrounding shells in a complicated pattern and suggest that its pressure is smaller than in those expanding regions. We discuss the locations of several HI and molecular clouds. Using comparisons between NaI and HI or CO velocities, in some cases we are able to improve the constraints on their distances. According to the velocity criteria, MBM 33−37, MBM 16−18, UT 3−7, and MBM 54−55 are closer than ∼100 pc, and MBM 40 is closer than 80 pc. Dense HI clouds are seen at less than 90 pc and 85 pc in the directions of the MBM 12 and MBM 41−43 clouds respectively, but the molecular clouds themselves may be far beyond. The above closest molecular clouds are located at the neutral boundary of the Bubble. Only one translucent cloud, G192−67, is clearly embedded within the LB and well isolated. These maps of the distribution of local neutral interstellar NaI gas are also briefly compared with the distribution of both interstellar dust and neutral HI gas within 300 pc.

Abundances for metal-poor stars with accurate parallaxes , I. Basic data

Abstract: We present element-to-element abundance ratios measured from high dispersion spectra for 150 field subdwarfs and early subgiants with accurate Hipparcos parallaxes (errors <20%). For 50 stars new spectra were obtained with the UVES on Kueyen (VLT UT2), the McDonald 2.7 m telescope, and SARG at TNG. Additionally, literature equivalent widths were taken from the works by Nissen & Schuster, Fulbright, and Prochaska et al. to complement our data. The whole sample includes both thick disk and halo stars (and a few thin disk stars); most stars have metallicities in the range −2 < (Fe/H) < −0.6. We found our data, that of Nissen & Schuster, and that of Prochaska to be of comparable quality; results from Fulbright scatter a bit more, but they are still of very good quality and are extremely useful due to the large size of his sample. The results of the present analysis will be used in forthcoming papers to discuss the chemical properties of the dissipational collapse and accretion components of our Galaxy.

Do X-ray binary spectral state transition luminosities vary?

Abstract: We tabulate the luminosities of the soft-to-hard state transitions of all X-ray binaries for which there exist good X-ray flux measurements at the time of the transition, good distance estimates, and good mass estimates for the compact star. We show that the state transition luminosities are at about 1-4% of the Eddington rate, markedly smaller than those typically quoted in the literature, with a mean value of 2%. Only the black hole candidate GRO J 1655-40 and the neutron star systems Aql X-1 and 4U 1728-34 have measured state transition luminosities inconsistent with this value at the 1σ level. GRO J 1655-40, in particular, shows a state transition luminosity below the mean value for the other sources at the 4σ level. This result, combined with the known inner disk inclination angle (the disk is nearly parallel to the line of sight) from GRO J 1655-40's relativistic jets suggest that the hard X-ray emitting region in GRO J 1655-40 can have a velocity of no more than about β = 0.68, with a most likely value of about β = 0.52, and a minimum speed of β = 0.45, assuming that the variations in state transition luminosities are solely due to relativistic beaming effects. The variance in the state transition luminosities suggests an emission region with a velocity of ∼0.2c. The results are discussed in terms of different emission models for the low/hard state. We also discuss the implications for measuring the dimensionless viscosity parameter α. We also find that if its state transitions occur at typical luminosities, then GX 339-4 is likely to be at a distance of at least 7.6 kpc, much further than typically quoted estimates.

Phase-induced amplitude apodization of telescope pupils for extrasolar terrestrial planet imaging

Abstract: In this paper, an alternative to classical pupil apodization techniques (use of an amplitude pupil mask) is proposed. It is shown that an achromatic apodized pupil suitable for imaging of extrasolar planets can be obtained by reflection of an unapodized flat wavefront on two mirrors. By carefully choosing the shape of these two mirrors, it is possible to obtain a contrast better than 10 9 at a distance smaller than 2λ/d from the optical axis. Because this technique preserves both the angular resolution and light gathering capabilities of the unapodized pupil, it allows efficient detection of terrestrial extrasolar planets with a 1.5 m telescope in the visible.

Dust emission from the most distant quasars

Abstract: We report observations of three SDSS z>6 QSOs at 250 GHz (1.2mm) using the 117-channel Max-Planck Millimeter Bolometer (MAMBO-2) array at the IRAM 30-meter telescope. J1148+5251 (z=6.41) and J1048+4637 (z=6.23) were detected with 250 GHz flux densities of 5.0 +- 0.6 mJy and 3.0 +- 0.4 mJy, respectively. J1630+4012 (z=6.05) was not detected with a 3 sigma upper limit of 1.8 mJy. Upper flux density limits from VLA observations at 43 GHz for J1148+5251 and J1048+4637 imply steeply rising spectra, indicative of thermal infrared emission from warm dust. The far-infrared luminosities are estimated to be \\~10^13 L_sun, and the dust masses ~10^8 M_sun, assuming Galactic dust properties. The presence of large amounts of dust in the highest redshift QSOs indicates that dust formation must be rapid during the early evolution of QSO host galaxies. Dust absorption may hinder the escape of ionizing photons which reionize the intergalactic medium at this early epoch.

Introducing GOLDMine: A new galaxy database on the WEB

Abstract: The new World Wide Web site "GOLDMine" (Galaxy On Line Database Milano Network) (http:// goldmine.mib.infn.it) contains a multiwavelength data-base of an optically selected sample of 3267 galaxies in the Virgo cluster and in the Coma Supercluster. It is designed for professional astronomers who wish to find data and images for these galaxies. Data gathered in 15 years of observational campaigns by the authors or taken from the literature include general parameters (catalogue names, celestial coordinates, morphological type, recessional velocity etc.), multiwavelength continuum photometry (total UV, U, B, V, J, H, K, FIR and radio magnitudes/flux densities), line photometry (HI, H2 ,H ), dynamical parameters (rotational velocity from the HI and H lines, velocity dispersion) and structural parameters (light concentration index, eective radius and brightness, asymptotic magnitude) in the optical (B and V) and Near Infrared (H or K) bands. Images include finding charts, optical (B and V), H, Near Infrared (H and/or K) and true color RGB frames (when available). Radial light profiles obtained from the B, V, H or K band images are also available. Integrated optical spectra along with broad Spectral Energy Distributions (SED) from the UV to the radio domain are given. All images can be obtained in JPG format, but the original (reduced) FITS images can be downloaded as well. The database will be updated regularly and will be extended to other local clusters and superclusters. Astronomers who wish to have their images included in GOLDMine are strongly encouraged to send us their material.